Radiofrequency (RF) tags and sensors are frequently used in national security applications, but radiofrequency sensing has numerous limitations. For instance, RF cannot penetrate metallic barriers and cannot be used in harsh environments (e.g., in water, in underground repositories, or in the presence of shelving). For safety reasons, RF cannot be used in the presence of high explosives. There are also operational hurdles, where RF tags and sensors can interfere with communications and are vulnerable to long-range interrogation by adversaries. Thus, the use of RF-based technologies can be limited for various technological, operational, or safety reasons.
Magnetoelastic tags are an alternative technology and are a familiar security measure used in stores to prevent theft. Current magnetoelastic tags are large, single frequency devices, cut from strips of an amorphous magnetic material, such as, Metglas® with low magnetostriction (about 12 to 30 ppm, based on its composition). They only convey information that a tag is magnetically activated, e.g., when passing through a portal, limiting their utility. These tags have limited frequency response and offer only “on” or “off” responses. In addition, these sensors must be machined and mounted to use, thereby increasing cost and decreasing utility.
Such magnetoelastic materials can be used to sense one or more conditions, such as a structural flaw or defect in buildings or aircraft s. Again, such sensors are limited by the lack of commercially available materials having high magnetostriction and capable of providing multiplexed signals.
Accordingly, there is a need for tags and sensors that can operate in various harsh or enclosed environments, as well as providing multiplexed responses. Alternatives to present RF and magnetoelastic technologies having enhanced functionality and lower manufacturing costs would greatly advance tagging and sensing modalities.